The invention relates to a method of manufacturing security elements for electronic article surveillance, The method includes the step of making the security elements of at least two layers. The present invention also relates to a security element manufactured according to the method.
From European patent EP 0 340 034 B1 there is known a security element for electronic article surveillance in warehouses and department stores which contains fibers of a material displaying high permeability and low coercive force. Either these fibers are contained in a paper substrate or they are affixed to the substrate by adhesive bonding. The orientation of the fibers in or on the substrate is completely arbitrary, as a result of which, there is a relatively high probability of the fibers overlapping with other fibers and coupling with them magnetically. The magnetic flux of the fibers is thereby concentrated and intensified, making it possible for the security elements described in the specification of the noted patent to be detected regardless of their orientation in relation to the interrogating field of the electronic article surveillance system.
It is an object of the present invention to provide a method for the manufacture of low cost and reliably operating security elements for electronic article surveillance.
This object is accomplished in that a first layer of a cellulose material is applied, in the still moist state, to a second layer of a cellulose material, with soft magnetic elements, which emit a characteristic signal in the interrogating field of an article surveillance system, being added to one of the two layers. The desired shape of the security elements is die stamped or cut out of the two layers in the dry state.
The advantage of the method of the present invention is to be seen mainly in the possibility for the layer with the soft magnetic fibers to be very thin because it is supported by the second thicker layer. Hence the layer with the soft magnetic fibers can be made of a highly dilute paper fiber suspension, which, as is described be hereafter in further detail, affords immense advantages as regards the subsequent orientation of the soft magnetic fibers and their processible length in the still moist cellulose material of the second layer. Furthermore, with both layers being applied to each other in the still moist state, they adhere firmly together after drying without the need of any additional steps, e.g., adhesive bonding the two layers.
According to a preferred further aspect of the method of the present invention, provision is made for the soft magnetic elements, which are fibers of very small diameter, to be oriented in essentially the longitudinal direction of the material web by external force applied when the fibers are in the moist state. In accordance with a particularly favorable embodiment of the method, this orientation is performed by providing a device, either above or underneath the layer of cellulose material containing the soft magnetic fibers, which produces a magnetic field in the longitudinal direction, meaning in the running direction of the material web. Because at this instant the cellulose material is in a still moist state, the fibers are oriented in the running direction of the material web under the action of the magnetic field. Alternatively, an orientation of the fibers in the running direction of the material web can also be effected forcibly by accelerating the layer of cellulose material with the integrated soft magnetic fibers; this results likewise in the fibers being oriented in the longitudinal direction of the layer.
The security element for electronic article surveillance produced by this method incorporates the following features: The first layer is a cellulose material comprised of cellulose fibers. The second layer is comprised likewise of a cellulose material made up of a mixture of cellulose fibers and soft magnetic elements. These soft magnetic elements are excited, as was previously mentioned in a magnetic interrogating field of an electronic article surveillance system to emit a characteristic signal.
As previously explained in connection with the method of the present invention, the magnetic elements are fibers made of a soft magnetic material. With a view to achieving as high a detection rate as possible it has proven advantageous for the length of the soft magnetic fibers to exceed 2 cm on average.
A preferred further aspect of the security element of the present invention provides for the cellulose material of the second layer to contain no more than half as many soft magnetic fibers as cellulose fibers. The superposed arrangement of two layers of cellulose material as disclosed in the present invention permits, in particular, the concentration of cellulose fibers contained in the layer with the soft magnetic fibers to be maintained at a very low level without detracting from stability. On account of the extremely dilute fiber suspension for the second layer this preferred embodiment of the security element of the present invention allows for
(a) relatively long magnetic fibers to be admixed to the cellulose material;
(b) the magnetic fibers to disperse well without excessive bending; and
(c) the magnetic fibers to be easily oriented by the application of external forces if required.
The present invention will be described in more detail in the following with reference to the accompanying drawing.